President Trump has canceled a visit next month to the United Kingdom. And this is a pretty big deal because the U.K. is considered America's closest ally. Many in London think he did this because he's worried about mass protests, but Trump says it is because the new embassy - which he was supposed to open - cost too much. He blamed President Obama. And said it was a bad deal when he was on Twitter. NPR's Frank Langfitt joins us from London.

Hi, Frank.

FRANK LANGFITT, BYLINE: Hey, David.

GREENE: OK. So do you know why the president is really canceling? Is it crowds? Is it this embassy deal? What is it?

LANGFITT: Well, there were big concerns about massive protests. If you remember, right after the president's inauguration, we had a version of the women's march. There was one here in London. Tens of thousands of people came out, jammed the streets, filled Trafalgar Square. So there were concerns about - protests would be even bigger.

But I spoke to somebody this morning who's familiar with how this all played out. And this person said the president actually did complain earlier this week that he didn't like Prime Minister Theresa May of the United Kingdom and that as a real estate developer, he thought the U.S. got a bad deal on the embassy. He didn't want to go to England. And so it seems to be that what he said on Twitter may well be true.

GREENE: So what is the backstory of this embassy?

LANGFITT: Well, you know, the United States sold the old embassy, which was located here in central London. It's prime real estate, just south of Marble Arch, east of Hyde Park. And Trump, as you were saying, blamed President Obama for not getting enough money for it. When he tweeted, he said, we sold it for peanuts. But the decision to move it was actually made under President Bush. It's been moved to a new location south of the Thames, which is more secure. And a big reason for this was to make it easier to protect against terrorism. President Trump says the new embassy cost $1.2 billion. But kind of, David, the big takeaway here is the president seems to see this visit - that was supposed to happen - to this big ally, in part, through the prism of his former job as a businessman and less as a politician or statesman.

GREENE: But there's also the relationship with Theresa May that might be at play here. Right? I mean, why is Trump so down on her?

LANGFITT: That seems to be another element. And the reason he's down on her is because she publicly criticized him. And as we know, the president of United States does not take public criticism lightly at all.

GREENE: Not well, no.

LANGFITT: No. And so after the president announced that the U.S. was going to move the embassy in Israel to Jerusalem, Prime Minister May broke with him and disagreed with him on it and said, you know, this is unhelpful to the peace process. The president didn't take it. He shot back on Twitter. And he said, you know, don't worry about U.S. policy. You need to focus more on fighting terrorism at home in the United Kingdom. And of course, this is after a year in which the U.K. suffered a series of terrorist attacks. So relations are - you know, seem to be a bit frosty right now.

GREENE: Well, these countries have gone through years of having different leaders from different parties. And....

LANGFITT: Sure.

GREENE: ...The relationship always seems close. I mean, how are people in London reacting to the idea that an American president would cancel a trip?

LANGFITT: He's deeply unpopular here. And most people this morning said they were glad that he's staying away. Our producer, Sam, went out to talk to people around Oxford Circus. And he talked to a woman named Anna Kayoko (ph). She's a retail manager at a major department store here in London. And here's what she said.

ANNA KAYOKO: Honestly, him not coming is good. U.K. don't need arrogance like that. U.K. don't need self-centered, ignorant people as Donald Trump, to be honest. We could do without people like that in the world.

LANGFITT: And another person that Sam talked to said, you know, I don't like him, but it is important this relationship with the U.S. - hoped that he would come, see the protests and understand how people here feel about him.

GREENE: Could he still come at some point?

LANGFITT: Oh, I think so. The prime minister's office said this morning that President Trump is welcome here and that he has accepted an invitation. Both sides, apparently, are trying for a working visit later this year before a state visit that would happen in the fall when President Trump would meet the queen.